Each type of social account that you can post to through Comity, has its own character limitations in place.
When posting to multiple profiles, Comity will enforce the lowest character limit of selected profiles. For example, if you try to share to Facebook & Twitter at the same time, you can only type up to 280 characters. If you try to share to Facebook & Linkedin then the limit will become 1300. You can overcome this limitation, by customizing posts after you schedule.